1. Field of the Invention
This invention relates to a laser beam transmitting apparatus for use in construction and civil engineering industries, and particularly to a laser beam transmitting apparatus for use for levelling using a laser beam and marking work along a horizontal plane or a vertical plane.
2. Related Background Art
There is known a laser beam level instrument as disclosed, for example, in U.S. Pat. No. 4,221,483. This laser beam level instrument converts light from a light source such as an He-Ne gas laser or a laser diode into a substantially collimated beam by an optical system having a collimator lens, and causes the beam to emerge in a horizontal direction by way of a rotatable mirror, thereby supplying a beam of light swept on a horizontal plane.
This apparatus according to the prior art will hereinafter be described with reference to FIG. 1 of the accompanying drawings.
A cylindrical inner housing 103 holding a collimator lens 105 is suspended from a beam transmitting unit 101 by means of three wires 102. The inner housing 103 is contained in a cylindrical fixed housing 104 fixed to the beam transmitting unit 101, and the outer peripheral surface of the inner housing 103 is spaced apart by a minute distance d from the inner peripheral surface of the fixed housing 104 and has the function of automatically correcting inclination within this range.
A light source 111 emitting a beam of light L is disposed substantially at the focal position of the collimator lens 105. A cylindrical rotatable member 114 is disposed below the collimator lens 105, and the rotatable member 114 is rotatably mounted on the beam transmitting unit 101 through a bearing 116. A pair of mirrors 115 for reflecting the beam of light L from the collimator lens 105 at a right angle are fixed to the interior of the rotatable member 114. The rotatable member 114 is rotated by a motor 110 through a transmission belt 118. The beam of light L reflected by the pair of mirrors 115 is caused to emerge outwardly through windows 114a and 101a and is swept in the direction of 360.degree. in a horizontal plane.
The beam transmitting unit 101 is placed on a levelling unit 130. The levelling unit 130 comprises an upper plate 131 fixed to the beam transmitting unit 101, and a lower plate 132 mounted on the upper plate 131 through three levelling screws 133. The lower plate 132 is connected to a tripod. A bubble tube 134 is fixed to the upper plate 131.
When installing the apparatus through the tripod, the operator turns the levelling screws 133 while watching the bubble tube 134 and effects rough levelling work. By this work, the operator can correct inclination up to the order of .+-.10' (minutes). When the manual levelling work by the operator is done, precise level accuracy within .+-.10" (seconds) is achieved by the above-described automatic inclination correction work of the inner housing 103.
However, the range within which the precise levelling by the automatic inclination correction is possible is as small as several tens of minutes and therefore, the levelling work of turning the levelling screws 133 while watching the positions of bubbles in the bubble tube 134 has required skill and has been practically cumbersome to the operator, and has taken much time until levelling is done up to an angle of several tens of minutes. Accordingly, when the laser beam transmitting apparatus is frequently moved for use, the burden of the operator has become greater, thus resulting in the aggravation of work efficiency.